The concept of inflatable seals for valves and more particularly inflatable seals that are used to seal the valve after the valve has been closed are known in the art. Some of the difficulties with the prior art inflatable seals are that they are not durable for use in abrasive environment and the sealing member recess often becomes contaminated with the particles being transferred thus requiring periodic flushing. The contamination problem is particularly troublesome if food materials are being transported since the accumulated food particles can contaminate the food and produce health risks. Another difficulty is that it is difficult to make a proper seal around the periphery of the butterfly disk and still provide an operable valve. While inflatable seals have been used with the axis of rotation of the valve offset from the valve seal, it has been found that such offset valves are prone to accumulation of material along the edges of the valve which may produce contamination in the system. Furthermore, valves with the axis of rotation offset from the seal provide for difficulty in opening or closing since the forces of the material acting on the valve surface create force imbalances making it difficult to oftentimes open and close the valve. In addition, such offset valves do not provide for equal flow since they provide a high profile that oftentimes interferes with the flow of material through the valve. In addition, such valves are often bulky and not suitable for use in high pressure large diameter material transportation systems.
Thus, one of the objectives of the invention is to provide an improved butterfly valve which cleanly and efficiently seals and, when retracted, has a low, clean profile that minimizes the opportunity for the transported material to accumulate particles in the valve and seal area. The present invention comprises an improvement to the inflatable seal butterfly valves by providing a new and improved seal.